This shader returns the absolute value of the dot product between the shading normal and the incoming ray direction. It is also named Incidence in other renderers. Unlike the Utility shader used in ndoteye mode, Facing Ratio works for any type of ray, not just camera rays. The returned values are always in the [0..1] range.

A tutorial that shows how to use the Facing Ratio to create a toon shader can be found here.

Push or pull values by altering the slope at the beginning of the range. Bias values below 0.5 decrease the slope and lower values overall. Above 0.5, the slope is higher, and the value grow's more quickly. A value of 0.5 has no effect.